A vehicle seat of an automotive vehicle is configured to deploy an airbag in case of accident when a passenger is seated on the seat and hence a load detection apparatus configured to detect the load of the passenger is provided. The vehicle seat is also configured to determine to be “seated” indicating that the passenger is seated when the load detected by the load detection apparatus exceeds a predetermined threshold value, and determine to be “not seated” when the load is not higher than the threshold value.
An example of a passenger sensing unit configured to determine the presence or absence of the passenger by sensing a load acting on the seat is described in JP 09-207638 A (hereinafter, referred to as Reference 1). In the passenger sensing unit disclosed in Reference 1, load sensors are installed only at two front and rear positions from among four seat mounting portions, whereby the presence or absence of the passenger is determined from the sum of the obtained two load values.
According to the passenger sensing unit described above, by mounting the load sensors at two positions at the front and the rear on the left or right side of the seat mounting portion, the presence or absence of the passenger may be determined while minimizing the number of positions of installation of the load sensors, and achieving cost reduction and weight reduction of the unit.
However, in a method of installing the load sensors at two positions on the front and the rear on the left or right side of the seat mounting portion, the load value to be detected by the load sensor in association with a turning travel of the vehicle varies, and there is a risk that erroneous determination is made. For example, when the load sensors are installed at two front and rear positions inside on a passenger seat side of a vehicle having a steering wheel on the left side, the load value detected by the load sensor is reduced by a centrifugal force that acts on the seat in association with the leftward turning travel of the vehicle. Therefore, distinction of whether the load value detected by the load detection apparatus is caused by unloading of the passenger or by the turning of the vehicle becomes difficult, and depending on the behavior of the vehicle, an airbag display lamp is continuously lit even though the passenger has gotten out of the vehicle.
Therefore, a seat passenger determination apparatus configured so as not to be associated with drawbacks as described above is desired.